The present invention relates to a glass substrate having two major surfaces and an infrared reflective coating disposed on each major surface. More particularly, the coated glass article has excellent heat resistant qualities and can be used as a heat barrier glass. This coated glass article has a particular application as at least one of the glass substrates in a view window of an oven, especially a self cleaning oven.
In the case of an oven door, one important quality is its ability to act as a heat barrier or heat sink. Ideally, a plurality of glass substrates inside the oven door should absorb the heat generated in the interior of the oven during use and transmit as little as possible of that heat to the exterior surface of the oven door. This is particularly important in the case of a self cleaning oven. Typically, the cook chamber of a self cleaning oven may reach temperatures as high as 482.degree. C. (900.degree. F.) during the self cleaning process. According to the Underwriters Laboratories Standards, the temperature of an outer surface of the outer most exterior glass of the window for a self cleaning oven may not exceed 77.degree. C. (170.degree. F.). Usually, oven manufacturers prefer to limit this exterior temperature of the outer surface of the outer most exterior glass to 60.degree. C. (140.degree. F.) or below.
Prior attempts to create a heat barrier glass include a plurality of glass substrates in a spaced apart relationship. In the case of a self cleaning oven, this is disclosed for example in U.S. Pat. No. 5,441,036. In accordance with this patent, four glass panes in a parallel and spaced apart relationship are provided. Channels are provided between the panes of glass. A fan is provided to force airflow through the channels. The forced air travels through the channels and absorbs some of the heat that would otherwise be transmitted to the panes of glass, and prevents it from radiating toward the exterior glass pane or exterior surface of the oven door. This patent also teaches the use of heat radiating fins in combination with the forced air flow.
In U.S. Pat. No. 4,951,652, a "getter" material is disclosed to reduce heat transmission. A double pane window assembly includes an evacuated space between the walls of the two panes of the window. The evacuated space is filled with a non-evaporable "getter" material. The "getter" material absorbs warm gases that are emitted from the internal pane of the window. However, this patent does not disclose utilizing such a system at temperatures typically encountered during self cleaning. Other known techniques include the use of a forced flow of a cooling fluid between adjacent panes of the view window, as in U.S. Pat. No. 3,192,575.
These previous attempts have not demonstrated satisfactory thermal performance regarding the necessary temperature drop across the view window during the self cleaning process. Also, many of the glass substrates that make up the discussed view window assemblies have an objectionable color. Furthermore, some of these same substrates include tong marks or other processing imperfections. Additionally, these prior attempts are relatively complex, expensive, and prone to breakdown.
The invention provides a view window that will act as a heat barrier to achieve a sufficient temperature drop across the view window and will exhibit superior thermal performance. It is also an object of the invention to provide a view window for the door of a self cleaning oven which exhibits a neutral color in reflectance. Furthermore, the invention will result in a view window which does not include tong marks or other processing imperfections associated with the discussed art. The invention also results in a simpler construction and less expensive view window. Lastly, the invention has exhibited excellent reliability.